This invention generally relates to a belt for supporting an elevator car.
An elevator has a car that is raised and lowered by a motor. Typically, a counterweight is used to offset the weight of the car so that the load on the motor is reduced. A belt connects the car to the counterweight and rests on a sheave. The belt obtains traction on the sheave, which is turned by the motor. Typically, the belt for the elevator car is composed of belt cords that support the weight of the elevator. These belt cords are very stiff along their length and are surrounded by a belt jacket that obtains traction on the sheave.
It has long been known in the industry that using a crown on a sheave will help the belt track toward the center of the sheave, even when the belt is slightly misaligned. While the crown may help the belt track better, the crown can degrade its performance. Specifically, due to the shape of the crown, pressure at the interface between the sheave and the belt is non-uniform. A high peak pressure will exist at the top of the crown, resulting in reduced life of the belt jacket and the belt cords.
In addition, because of the stiffness of the belt cords, these cords tend to move at the same speed. The speed of the sheave surface is directly proportional to the distance between a centerline of the sheave and its surface. Consequently, the peak of the crown travels at a higher circumferential speed than the remainder of the sheave surface. Because the belt cords all move at the same speed, and the speed of the sheave surface varies due to the crown, there are locations where the belt surface and the corresponding sheave surface will have different speeds. As a consequence, there is localized slipping between the belt surface and the sheave surface, resulting in belt wear.
A need therefore exists for a belt having a profile that accommodates the shape of the crown of the sheave.